The invention relates generally to the on-line use of combined nephelometric and directional sky radiance systems in a novel electro-optical device for real time monitoring of the optical state of the atmosphere.
As the deployment of tactically oriented electro-optical systems becomes increasingly commonplace, there is a continuing and concomittant requirement for understanding those environmental factors most influencing their performance. In many cases, it is the influence of poor weather conditions upon visible and infrared transmittance that is a primary factor in degrading the performance of the electro-optical systems.
The primary data base upon which many visible spectrum atmospheric models have been built consists mainly of selected profile measurements of volume scattering coefficients and 4.pi. radiance distributions. The C-130 class nephelometer (see Johnson et al, "Measurements of Optical Atmospheric Quantities in Europe and Their Application to Modelling Visible Spectrum Contrast Transmittance", Proceedings of the AGARD 29th Symposium of the Electromagnetic Wave Propagation Panel on Special Topics in Optical Propagation, Vol. AGARD-CP-300, pp 14-1 to 14-12 (1981); and Johnson, "Daytime Visibility and Nephelometer Measurements Related to its Determination", Atmospheric Environment, Vol 15, No 10/11 pp 1835-1845 (1981)) measured both the total volume scattering coefficient, and the directional scattering function at 30.degree. and 150.degree.. Although this data base has provided a substantial quantity of excellent quality data for both general modelling and specific slant path contract transmittance determinations, its acquisition and manipulation have been expensive and time consuming operations. A compact, reliable, and simple electro optical system that would provide additional directional scattering and sky radiance data is required.
The airborne instrument system of the present invention fulfills the foregoing described need by providing a novel airborne instrument system for providing real-time outputs of atmospheric directional contrast transmittance values utilizing a simplified computational procedure. The system of the invention provides an output which is the slant path contrast transmittance along any preselected path of sight within the sampled environment. The invention is primarily intended for airborne application within the lower troposphere, but is easily adaptable for static ground based application in the determination of surface directional visibilities. The system of the invention provides the needed atmospheric transmittance information to support a broad variety of activities related to military tactical operations, meteorological forecasting procedures and fundamental research into the optical properties of the atmosphere.
It is, therefore, a principal object of the present invention to provide an improved atmospheric contrast transmittance monitor.
It is a further object of the invention to provide a novel airborne system for providing real time outputs of directional atmospheric contrast transmittance functions.
It is yet another object of the invention to provide a novel contrast transmittance monitor for providing directional scattering data uniquely appropriate for this application.
These and other objects of the present invention will become apparent as the detailed description of certain representative embodiments thereof proceeds.